Method and apparatus for automated docking of a test head to a device handler

ABSTRACT

A positioner facilitates docking and undocking of an electronic test head with a device handler. The positioner provides for rotation of the test head about a first axis. The positioner includes a linkage arm structure for moving the test head along a second axis orthogonal to the first axis. Using motors, sensors and a processor, the linkage arm structure accurately docks the electronic test head with the device handler.

This application is a division of U.S. patent application Ser. No.08/355,501, filed on Dec. 12, 1994, now U.S. Pat. No. 5,600,258, whichis a continuation-in-part of U.S. patent application Ser. No.08/122,055, filed Sep. 15, 1993, now U.S. Pat. No. 5,440,943.

A microfiche Appendix is included in this application containing 1microfiche. The microfiche contains 93 frames plus one test target framefor a total of 94 frames.

A portion of this patent document contains material which is subject tocopyright protection. The owner has no objection to the facsimilereproduction by anyone of the patent document or patent disclosure as itappears in the Patent and Office patent file or records, but otherwisereserves all rights whatsoever.

FIELD OF THE INVENTION

This invention relates to the field of art of electronic test headpositioners.

BACKGROUND OF THE INVENTION

In the automatic testing of integrated circuits (IC) and otherelectronic devices, special device handlers have been used which bringthe device to the proper temperature and place the device to be testedin position. The electronic testing itself is provided by a large andexpensive automatic testing system which includes a test head which hasbeen required to connect to and dock with the device handler. In suchtesting systems, the test head has usually been very heavy--on the orderof 40 to 300 kilograms. The reason for this heaviness is that the testhead uses precision high frequency control and data signals so that theelectronic circuits may be located as close as possible to the deviceunder test. Accordingly, the test head has been densely packaged withelectronic circuits in order to achieve the accurate high speed testingof the sophisticated devices.

Test head positioner systems may be used to position the test head withrespect to the device handler. When the test head is accurately inposition with respect to the device handler, the test head and thedevice handler are said to be aligned. When the test head and devicehandler are aligned, the fragile test head and device handler electricalconnectors can be brought together (i.e. docked), enabling the transferof test signals between the test head and the device handler. Prior todocking, the fragile test head and device handler electrical connectorsmust be precisely aligned to avoid damaging the fragile electricalconnectors.

A positioner, able to move along a support structure, carries the testhead to the desired location at which the test head is positioned toconnect to and dock with the device handler. The test head is attachedto the positioners so that the test head can achieve up to six degreesof motion freedom (X, Y, Z, θX, θY, θZ).

Test heads, and their respective positioners, are often used in anultraclean room environment. However, ultraclean room environments areoften extremely expensive to provide. Thus, the useable space within anultraclean environment is only available at a premium.

A variety of test head manipulators are currently available for use inultraclean room environments. Although some of these test headmanipulators have a variety of desirable features, the amount of spacewhich each of these test head manipulators requires for proper operationmay be undesirable.

As device testing in general, and the use of test heads and devicehandlers in particular becomes developed to handle ever moreincreasingly complex tasks, test heads continue to get larger andlarger. This increase relates both to the physical size and weight ofthe test head. However, as test heads get larger and larger, fullymanual, fully balanced methods become ever more difficult to actuallyimplement in hardware.

SUMMARY OF THE INVENTION

A positioner facilitates docking and undocking of an electronic testhead with a device handler. The positioner provides for rotation of thetest head about a first axis. The positioner includes a linkage armstructure for moving the test head along a second axis orthogonal to thefirst axis. Using motors, sensors and a processor, the linkage armstructure accurately docks the electronic test head with the devicehandler.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective drawing which illustrates an exemplaryembodiment of the present invention.

FIG. 2 is a perspective drawing which illustrates a gantry which forms apart of an exemplary embodiment of the present invention. Theperspective drawing provides a view from the bottom of the gantry.

FIG. 3 is a perspective drawing which illustrates coupling between acradle back (which provides roll motion) and a carriage base.

FIG. 4 is a perspective drawing which illustrates coupling between aswing arm and a carriage base.

FIG. 5 is a further perspective drawing which illustrates an exemplaryembodiment of the present invention.

FIG. 6a is a perspective drawing which illustrates coupling between aswing arm support in accordance with a further exemplary embodiment ofthe present invention.

FIGS. 6b and 6c are side views of the cradle support shown in FIG. 6a.

FIG. 7a is a perspective view of an exemplary embodiment of the presentinvention.

FIG. 7b is an exploded perspective drawing which illustrates couplingbetween a linkage arm structure and a carriage rail.

FIG. 8 illustrates the Y-drive assemble according to an exemplaryembodiment of the present invention.

FIG. 9 is a perspective drawing which illustrates docking of a test headto a device handler in accordance with an exemplary embodiment of thepresent invention. The perspective drawing provides a view from thebottom of the test head and the device handler.

FIG. 10 is a perspective view which illustrates docking of the alignmentpin on the device handler to the alignment hole in the protection plateon the test head.

FIG. 11 is a perspective view of the enclosure which contains theelectronic components for docking the test head with the device handlerin accordance with an exemplary embodiment of the present invention.

FIG. 12 is a block diagram which illustrates the operation of theelectronic components included in an exemplary embodiment of the presentinvention.

FIGS. 13a and 13b are perspective drawings which illustrate calibrationof alignment structures with regard to the device handler and the testhead, respectively.

FIG. 13c is a flow chart diagram which illustrates programming of theprocessor system for performing automatic docking.

FIG. 14 is a flow chart diagram which illustrates manipulation of thetest head during automatic docking.

FIGS. 15-30 are flow chart diagrams which explain operation of theprocessor system.

FIGS. 31a-c illustrate alternative embodiments of the present invention.

FIG. 32 illustrates the placement of linear variable displacementtransducers in accordance with an alternative embodiment of the presentinvention.

FIG. 33 diagrammatically shows the six degrees of freedom of the systemshown for example in FIGS. 1, 4 and 5.

OVERVIEW

The present invention relates to a positioner system 200 forautomatically docking an electronic test head 110 with respect to anintegrated circuit handler 120. When test head 110 and device handler120 are docked, the very fragile contacts 14 located on test head 110are very precisely aligned and mated with connectors 15 on devicehandler 120. Positioner system 200 moves the test head 110 under motorcontrol with precise movements to mate contacts 14 and connectors 15.Furthermore, various positional sensors (described below) ensure thatcontacts 14 and connectors 15 are not misaligned prior to being mated.

As shown for example by FIG. 1, test head 110 (shown in phantom) iscoupled to cradle 112. Inclinometer 512 provides signals which indicatethe position of test head 110 about the Y axis (see FIG. 31). Cradle 112is coupled to test head drive assembly 130. As shown in FIG. 3, testhead drive assembly 130 includes stepper motor 132 which rotates cradle112 about the Y axis. Support member 46 couples test head drive assembly130 to swing arm 37. Wrist shaft 36 extends through an opening in swingarm 37 and engages wrist block 34 (and enables movement about the Zaxis). As shown in FIG. 5, side to side shafts 35a,b extend throughopenings in carriage base 26 to enable movement along and about the Xaxis. As shown in FIG. 7a, carriage base 26 slides along in-out shafts25a, 25b for movement along the Y axis. In-out shafts 25a, 25b arecoupled to carriage rails 22a, 22b. Carriage rails 22a, 22b are situatedat the bottom of linkage arms 20. Linkage arms 20 each form a scissorshaped member. As motor 212 rotates ball screw 41, the top portion oflinkage arm structures 20a, 20c are moved either towards or away fromthe top portion of linkage arm structures 20b, 20d. This results incarriage rails 22a, b moving upward and downward as the bottoms oflinkage arm structures 20 swing upward and downward (by virtue of thetops of linkage arm structures 20 moving towards and away from eachother). Test head 110 is thus moves upward and downward.

As shown in FIG. 9, protection plates 1012 are attached to test head110. When alignment holes 1020 formed in protection plates 1012 receivealignment pins 1005 attached to device handler 120, test head 110 isproperly aligned with device handler 120. Test head 110 and devicehandler 120 may then be docked without destroying contacts 14 includedin test head 110.

Linear Variable Distance Transducers (LVDTs) 1015 are also attached toprotection plates 1012. As test head 110 is moved towards device handler120, the sensory "pin" extending from each LVDT is compressed inwards.Each LVDT then generates a signal indicating the distance by which eachsensory pin is compressed.

During installation (before test head 110 is ever docked to devicehandler 120) calibration fixtures 1313, 1314 (see FIGS. 13a, b) are usedto precisely align alignment pins 1005 and alignment holes 1020 withregard to each other and with regard to contacts 14 and connectors 15.Each calibration fixture is first positioned relative to a mechanicaltarget on the respective test head 110 and device handler 120. Alignmentpins 1005 and alignment holes are then positioned relative to alignmentstructures formed in the calibration fixtures. Each LVDT is thensituated so that each LVDT's sensory pin is compressed inwards untileach LVDT provides a predetermined reading. This reading is defined tocorrespond to test head 110 and device handler 120 being relativelypositioned to barely achieve contact between contacts 14 and connectors15.

Test head 110 and device handler 120 are then brought together (i.e.using motorized or manual motion from positioner system 200) so thatalignment holes 1020 receive alignment pins 1005 and each LVDT generatesthe predetermined reading described above. The non-motorized degrees offreedom of positioner system 200 are fixed. Test head 110 is then movedby motor towards device handler 120 a predetermined distance asindicated by the LVDTs to achieve, for example, desired insertiondistance of contacts 14 in connectors 15 (or if contact 14 is a springtype pogo pin, desired distance of compression of contact 14). Thesignals generated by the LVDTs are then stored.

During automated motorized docking, the initial position of the testhead is determined from the signals generated by inclinometers 510, 512.After test head 110 is lowered by motor 212 so as to be close enough todevice handler 120 for the LVDTs to register, the LVDT signals are usedto accurately determine the position of test head 110 relative to devicehandler 120. If test head 110 is not properly aligned about the Y axiswith device handler 120 prior to docking, the signals generated by theLVDTs will so indicate. Motor 132 can then be actuated until prioralignment is achieved and test head 110 and device handler 120 may thenbe docked.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, there is shown a test head positioner system200 in accordance with an exemplary embodiment of the present invention.As shown, positioner system 200 carries a test head 110 with contacts 14for a test system for docking with connectors 15 of an integrated device(circuit) handler 120. Contacts 14 may be pogo pins (collapsible,spring-like pins) or static pins (e.g., as in a Hypertac connectorarrangement). It will be understood that other electronic devices may behandled by the device handler, such as transistors, chips or dies, etc.In operation, positioner system 200 moves test head 110 accurately andprecisely so that it may be docked to handler 120. Docking may beaccomplished, for example, as more fully described in a previous patentby Smith (U.S. Pat. No. 4,705,447), herein incorporated by reference,and in a previous patent by Holt (U.S. Pat. No. 4,893,074), which isherein incorporated by reference. As will be described in detail, theposition of test head 110 may be accurately manipulated to anotherposition with six degrees of freedom X, Y, Z, θX, θY, θZ as shown inFIG. 33.

It is important for the proper installation of test head 110 that ithave six degrees of freedom so that it can accurately be positioned withrespect to handler 120. Furthermore, the motion of test head 110 can berestricted so that it automatically moves under motor control with onlytwo degrees of motion (for example θY, Z). In this manner, test head 110can be readily undocked and redocked with handler 120, so thatmaintenance of test head 110 can be performed.

In an exemplary embodiment of the present invention, test head 110 maybe mounted via a yoke 112 to test head drive assembly 130. By use oftest head drive assembly 130, test head 110 is able to rotate at least180° about an axis which shall be defined as a Y axis. The ability oftest head 110 to rotate about the Y axis facilitates maintenance of testhead 110 as will be more fully described below.

Positioner assembly 200 includes a gantry 300, the details of which areshown in FIG. 2. There are provided two beams 42a, 42b and two carriagerails 9, 10 forming the top of the gantry. Two legs 43b, 43d areattached to beam 42b at opposite ends so as to support beam 42b apredetermined distance from the floor. In addition, two legs 43a, 43care disposed at opposite ends of beam 42a to support beam 42a at apredetermined distance from the floor. At the bottom of each leg 43a,43b, 43c, 43d, a leveling pad (not shown) may be installed to facilitateleveling of the gantry. Alternatively, the gantry (without, for example,legs) could be suspended from the ceiling over the integrated circuithandler 120. An operator terminal 48 is also included. In an exemplaryembodiment of the present invention, operator terminal 48 is model 550manufactured by Allen Bradley Corporation. The operator terminal iscoupled to beam 42b by hanger assembly 49.

A light curtain assembly is also included. The light curtain assemblyincludes (infrared light) transmitter 91, mirror assemblies 92, 93 andreceiver 94. When the light beams generated by transmitter 91 andreceived by receiver 94 are interrupted, all motorized functions arestopped. In this manner, risk of injury to a worker by the motorizedsystem is reduced.

As shown in FIG. 3, test head drive assembly 130 is coupled to supportmember 46. Support member 46 may be, for example, a rectangular beam ora goose neck as shown in FIG. 3 (depending upon the path of cablesleaving the test head). Support member 46 may be coupled, in turn, toswing arm 37. Swing arm 37 is desirably of proper length so that whentest head 110 is coupled to positioner system, test head 110 is in abalanced state (i.e. at its approximate center of gravity) with regardto the non-motorized degrees of freedom. Swing arm 37 is coupled tosupport member 46 at substantially right angles.

Test head drive assembly 130 comprises stepper motor 132,(electromagnetic) brake 131 attached thereto, gear box 133 with gears(not shown) being driven by stepper motor 132, helical gears 134attached to and rotated by gear box 133 and limiting switch 135 attachedto helical gears 134. In an exemplary embodiment of the presentinvention, motor 132 is model M111-FF-206E manufactured by SuperiorElectric Corporation.

Side-to-side shafts 35a, b are each coupled to wrist block 34 atrespective openings. Thus, wrist block 34 is stationary relative toside-to-side shafts 35a, b. An additional opening is situated in thebottom of the wrist block 34. Wrist shaft 36 extends from the opening inthe bottom of wrist block 34 through a further opening in swing arm 37.Wrist shaft 36 is coupled to wrist block 34. A flange 136 may besituated at the opposite end of wrist shaft 36 supporting swing arm 37.Wrist shaft 36 defines a Z axis. Swing arm 37 rotates about the Z axisby rotating relative to wrist shaft 36. Thrust bearing 80 (not shown),situated between the flange of wrist shaft 36 and swing arm 37facilitates rotation of swing arm 37. Movement of swing arm 37 about theZ axis may be prevented by actuating lock wrench 3.

Wrist shaft 36 is coupled to carriage base 26. Coupling between wristshaft 36 and carriage base 26 is illustrated by FIG. 4.

As shown in FIG. 4, carriage base 26 includes rectangular opening 103and rectangular opening 104. Wrist shaft 36 extends between wrist block34 and swing arm 37 by going through rectangular opening 103. Extensionmember 502 (extending from wrist block 34) extends through rectangularopening carriage walls 29a, 29b, 29c, 29d (not shown) which may be anintegrally formed part of carriage base 26 are situated aboutrectangular opening 103. Carriage ceiling 29e (not shown) may besituated on top of carriage walls 29a-d to form a partially enclosedspace. Side-to-side shaft 35a extends through carriage wall 29a.Similarly, side-to-side shaft 35b extends through carriage wall 29b.

Side-to-side shafts 35a, 35b, define an X axis. Thus, wrist block 34 isable to move along the X axis by the sliding motion of side-to-sideshafts 35a, 35b. Wrist block 34 is also able to move about the X-axisdefined by side-to-side shafts 35a, b. Movement of wrist block 34 bothalong and about the X-axis is facilitated by bearings 72a, 72b which maybe situated, for example, adjacent to carriage walls 29a, 29brespectively.

As shown in FIG. 5, extension member 502 extends outwardly from wristblock 34. Extension member 502 extends through opening 104 and iscoupled to lock collar 508. Lock screw 503 couples together extensionmember 502 and lock collar 508. As previously stated, test head 110 iscapable of rotating about the X axis defined by side-to-side shafts 35a,35b. Movement of test head 110 about the X axis may be prevented byactuating lock wrench 503.

Lock collar 508 is also used for preventing movement of test head 110along the X axis. As previously stated, wrist block 34 is able to movealong the X axis by side-to-side shafts 35a, 35b. Lock wrench 512extends from the bottom of carriage base 26, through a slot formed incarriage base 26, and into lock collar 508. When lock wrench 512 is notactuated, movement of lock collar 508 with wrist block 34 (and hencetest head 110) along the X axis is facilitated by cam follower 514(which is mounted onto lock collar 508) sliding along cam followerreceptacle 518 (which is mounted onto the top surface of carriage base26). Movement of test head 110 along the X axis may be prevented byactuating lock wrench 512.

FIG. 6a illustrates an alternative embodiment of the present invention.Y translation lock brackets 610a, 610b are coupled to horizontal rail 51through appropriate fasteners (not shown) which extend into Ytranslation lock brackets 610a, 610b through slots 605 formed inhorizontal rail 51 (described in more detail with regard to FIG. 7a).Rear brackets 610a, 610b are capable of moving along respective slots605 and are then fastened securely into place. θX lock bracket 620a iscoupled to Y translation lock bracket 610a through an appropriatefastener (not shown) which extends into θX lock bracket 620a throughslots 612 formed in Y translation lock bracket 610a. Similarly, θX lockbracket 620b is coupled to Y translation lock bracket 610b throughfastener 628. θZ lock member 650 includes side portions 652, 654 andbottom portion 656. Side portion 652 is coupled to θX lock bracket 620aby fastener (not shown) which extends through a slot formed in θX lockbracket 620a. Side portion 654 is coupled to θX lock bracket 620b byfastener 628 which extends through a slot formed in θX lock bracket620b. Swing arm 37 rests on bottom portion 656. Fasteners (not shown)extend from the bottom of bottom portion 656, through slots 651 inbottom portion 656 and into swing arm 37. Swing arm 37 is coupled tospindle block 34 and to the test head drive assembly 130 as described inthe text which refers to FIG. 3.

Pitch adjust screws 615a, b extend through threaded openings inextension members 630 which are attached to and project from sideportions 652, 654. The bottom end of pitch adjust screws 615a, b makecontact with the bottom surfaces of projections 640a, b extending fromθX lock brackets 620a, b.

The various components described above are capable of various types ofmovements relative to each other. These various movements cause swingarm 37 to move. The movement of swing arm 37 in turn causes test head110 to move. In this manner, test head 110 can be aligned with devicehandler 120 for proper docking and undocking of test head 110 to devicehandler 120. For example, loosening bolts extending through openings 605enables movement of test 110 along the X axis. Loosening bolts 612enables movement of test head 110 along the Y axis. Loosening bolts 630and actuating pitch adjust screws 615 a, b results in motion of testhead 110 about the X axis (as shafts 35a, b pivot within bearings 72a,b). Loosening bolts extending through slots 651 and into swing arm 37results in enabling motion of test head 110 about the Z axis (as swingarm 37 rotates about wrist shaft 36).

FIGS. 6b and 6c illustrate how swing arm 37 pivots about the X axis aspitch adjust screws 615a, b are actuated. FIG. 6b illustrates pitchadjust screw 615a extending as far as possible through extension member630. Because of the relatively large distance between extension member630 and the bottom surface of projection 640a, the rear of swing arm 37tilts downwards and the front of swing arm 37 tilts upwards. Becausetest head 110 is coupled to the front portion swing arm 37, test head110 tilts upwards (i.e., pivots upwards or counterclockwise to theposition shown in FIG. 6b). FIG. 6c illustrates pitch adjust screw 615aextending as little as possible through extension member 630. Because ofthe relatively small distance between extension member 630 and thebottom surface of projection 640a, the rear of swing arm 37 tiltsupwards and the from the swing arm 37 tilts downwards. Test head 110thus tilts downwards (i.e., pivots downwards or clockwise to theposition shown in FIG. 6c).

As shown in FIG. 7a, bearing blocks 30a, 30b, 30c, 30d (included incarriage base 26) enables carriage base 26 to be coupled to carriagerails 22a, b. Specifically, pillow blocks 24a, b are coupled to carriagerail 22a by each extending from the surface of carriage rail 22a.Similarly, pillow blocks 24c, d are coupled to carriage rail 22b by eachextending from the surface of carriage rail 22b. In-out shaft 25aextends from pillow block 24a to pillow block 24b and is held inposition by retaining rings 69a, 69b (not shown). In-out shaft 25bextends from pillow block 24c to pillow block 24d and is held inposition by retaining rings 69c, 69d (not shown). In-out shaft 25aextends through lock collar 32 which is also coupled to carriage base26. Carriage rails 22a, 22b are coupled together by horizontal rail 51.

In-out shafts 25a, b each define a Y axis. Thus, carriage base 26 iscapable of moving along the Y axis as a result of bearing blocks 30a, b,c, d sliding along in-out shafts 25a, b. The Y axis movement isfacilitated by bearings 79 mounted in bearing blocks 30a, b, c, d.Movement of carriage base 26 along the Y axis may be prevented byactuating clamping knob 4b, shown coupled to lock collar 32.

As shown in FIG. 7a, linkage arm 20 (shown to the left in the figures)includes linkage arm structure 20a and linkage arm structure 20b.Linkage arm 20 (shown to the right in the figures) includes linkage armstructure 20c and linkage arm structure 20d. Linkage axle 33 includesends of diminished diameter which extend through openings in linkage armstructures 20a, 20c and is coupled to carriage rails 22a, 22b. In thisway, linkage arm structures 20a, 20c are coupled to carriage rails 22a,22b.

Linkage axle 21 also includes ends of diminished diameter. This is moreclearly shown in FIG. 7b. One end of linkage axle 21 extends through anopening near the bottom of arm component 20b, and through a furtheropening in trolley 17a. A similar configuration may be found on theopposite end of linkage axle 21 which extends through an opening inlinkage arm structure 20d, and through an opening in a further trolley17b (not shown). Each trolley 17a, b includes cam followers 76 whichengage the slots in carriage rails 22a, b and thrust bearings 75 whichmake contact with carriage rails 22a, b. Cam followers 75, 76 facilitatemovement of trolleys 17a, 17b relative to carriage rails 22a, b. As theleft-most and right-most linkage arms function and are coupled to theremaining apparatus similarly, the operation of linkage arm structures20a, 20b only will be described.

Linkage arm structure 20a and linkage arm structure 20b are coupledtogether by pivot pin 18. Movement of linkage arm structure 20a relativeto linkage arm structure 20b is facilitated by needle bearing 84 (notshown).

Linkage arm structure 20a is capable of a limited amount of rotationabout linkage axle 33. Furthermore, linkage arm structure 20b is capableof a limited amount of rotation about linkage axle 21. This rotation isuseful for vertical motion of test head 110 along the z axis as will bedescribed later.

As shown in FIG. 8, motor 212 is included. In an exemplary embodiment ofthe present invention, motor 212 is model M113-FF-4011 manufactured bySuperior Electric Corporation. Motor 212 rotates gear box 113. Rotationof gear box 113 may be selectively prevented by the actuation of brake115. Gear box 113 rotates ball screw 41 (via shaft coupling 42). As ballscrew 41 rotates, ball nut 114 moves along the axis defined by ballscrew 41. Ball nut 114 is coupled to ball screw axle 16. As shown inFIG. 7a, ball screw axle 16 includes a shoulder at each end whichprojects through respective holes in linkage arm structures 20a, 20d andtrolleys 17c, d. Trolleys 17c, d each include cam followers 76 whichengage and move along respective tracks which are formed in carriagerail 9 and horizontal member 8 (shown in FIG. 1 between carriage rails9, 10. Limit switches 80a,b mounted on the inner vertical surface ofcarriage rail 9 are used to detect whether trolley 17c has reached thetrack limits. Trolleys 17c, d each also include cam followers 75 whichcontact and facilitate movement relative to carriage rails 8, 9 asdescribed below. Linkage arm structures 20b rotate about pivot pin 19.Each pivot pin 19 is fixed to horizontal member 8 and carriage rail 9,respectively. This rotation facilitates vertical movement of test head110 along the z axis as described below.

Inclinometer 510 is attached to a vertical surface of linkage armstructure 20b. Inclinometer 512 is attached to a vertical surface ofyoke 512 (see FIG. 1). In an exemplary embodiment of the presentinvention, inclinometers 510 and 512 are each Model A2-A-1, manufacturedby U.S. Digital Corporation.

Vertical motion of test head 110 (i.e. motion along the Z axis) isaccomplished as follows. As motor 212 turns, ball screw 41 also turns.This results in motion of ball nut 114 along the axis defined by ballscrew 41. As ball nut 114 moves along the axis defined by ball screw 41,ball screw axle 16 (through trolleys 17c, 17d with cam followers 76)moves along horizontal member 8 and carriage rail 9. This, in turn,results in the movement of the top portion of linkage arm structures20a, 20c along horizontal member 8 and carriage rail 9. As the upperportions of linkage arm structures 20a, 20c move along horizontal member8 and carriage rail 9, the bottom portion of linkage arm structures 20a,20c also moves. This motion of the bottom portion of linkage armstructures 20a, 20c is vertical. The vertical motion of linkage armstructures 20a, 20c results in the vertical movement of carriage rails22a, 22b. As the front portion of carriage rails 22a, 22b movesvertically, the rear portion of carriage rails 22a, 22b also movesvertically. As carriage rails 22a, 22b move vertically, test head 110moves vertically as well. Thus, the linkage arm structures 20a, b, c, dprovide a lifting mechanism while at the same time determining the pathof motion of test head 110.

Tilt of test head 110 (i.e., motion about the Y axis) is accomplished byengaging test head drive assembly 130. As motor 132 in test head driveassembly 130 rotates, yoke 112 (and hence test head 110) rotates aboutthe Y axis.

FIGS. 9 and 10 illustrate docking of test head 110 to device handler120. As shown in FIG. 9, docking is accomplished by test head 110 beingmoved (for example, downward) toward device handler 120 so that fragileelectrical contacts 14 on test head 110 which are aligned by alignmentpins 1005 and alignment holes 1020 make precise contact with connectors15 on device handler 120.

Plural alignment pin bases 1007 are mounted on device handler 120 (forexample, on the top surface of device handler 120). A respectivealignment pin 1005 is mounted on the top surface of each alignment pinbase 1007. Each alignment pin 1005 has a tapered upper end.

Plural protection plates 1012 are mounted on test head 110 (for example,adjacent to the contact side surface of test head 110). Each protectionplate 1012 includes respective alignment hole 1020 which mates withrespective alignment pin 1005.

Directly below each alignment pin 1005 is located respective load cell1010. In an exemplary embodiment of the present invention, load cell1010 is model ELF-TC-1000-250 manufactured by Entran Corporation. Iftest head 110 is being accurately docked with device handler 120, eachalignment pin 1005 will be centered relative to respective alignmenthole 1020. If alignment pin 1005 is not centered relative to respectivealignment hole 1020 (indicating that test head 110 is not accuratelyaligned to device handler 120) load cell 1010 will indicate a loadduring docking. Thus, each load cell 1010 is provided as a safetyprecaution.

A respective Linear Variable Displacement Transducer (LVDT) 1015 is alsocoupled to each protection plate 1012. LVDTs 1015 are labelled LVDT1,LVDT2, LVDT3 and LVDT4 for case of identification. In an exemplaryembodiment of the present invention, each LVDT 1015 is model GCD-121-250manufactured by Schaevitz Corporation. As each LVDT 1015 makes contactwith the respective alignment pin base 1007 and test head 110 is furtherlowered with respect to device handler 120, a spring loaded "pin" shownextending from the bottom of each LVDT 1015 is pressed into the interiorof LVDT 1015. In other words, each LVDT 1015 is compressed. As each LVDT1015 is compressed, each LVDT 1015 generates a signal indicative of thedistance by which each LVDT 1015 is compressed (i.e.compression--distance). The distance by which each LVDT 1015 iscompressed provides an indication of the distance between test head 110and device handler 120 to guide precise docking.

During the course of initial mechanical installation and before the testhead 110 and device handler 120 are docked for the first time (i.e.before any programming or "teaching" of the electronics to performautomated docking of test head 110 to device handler 120 and beforeactual automated docking of test head 110 to device handler 120 for thefirst time), device handler calibration fixture 1314 (shown in FIG. 13a)and test head calibration fixture 1313 (shown in FIG. 13b) are used tocalibrate alignment pins 1005 relative to alignment holes 1020. In thisway test head 110 and device handler 120 may be aligned to preventdamage to fragile contacts 14 during the docking procedure.

Device handler calibration fixture 1313 is used to properly positionalignment pins 1005 relative to alignment holes 1020. In order toproperly position alignment pins 1005, screws securing each alignmentpin base 1007 to device handler 120 are loosened so that limitedmovement is possible between each alignment pin base 1007 and devicehandler 120. Device handler calibration fixture 1313 is then set on topof device handler 120. Device handler calibration fixture 1313 includesreference features 1320 (e.g. pins) which can be aligned to (or engage)reference features 1321 (e.g. openings) included in device handler 120.In this way, device handler calibration fixture 1313 is alwaysidentically positioned when it is set on top of the same device handler120.

Device handler calibration fixture 1313 includes a plurality ofcalibration opening 1322. Each alignment pin base 1007 is moved so thateach alignment pin 1005 precisely engages a respective calibrationopening. Because of the tapered shape of each alignment pin 1005, if anyalignment pin 1005 is not precisely positioned relative to therespective calibration opening 1322, load cell 1010 will indicate aload. Thus, the output of each load cell 1010 can be checked to ensurethat each alignment pin 1005 is properly positioned. Once each alignmentpin 1005 is properly positioned, the screws holding each alignment pinbase 1007 are tightened, and device handler calibration fixture 1313 isremoved.

Test head calibration fixture 1314 is used to properly positionalignment holes 1020 relative to previously positioned alignment pins1005. In order to properly position alignment holes 1020, test head 110is rotated so that contacts 14 face upwards. The screws securing eachprotection plate 1012 to test head 110 are loosened so that limitedmovement is possible between each protection plate 1012 and test head110. Test head calibration fixture 1314 is then set on top of test head110. Test head calibration fixture 1314 includes reference features 1322(e.g. openings) which can be aligned to (or be engaged by) referencefeatures 1323 (e.g. pins) included in test head 110. In this way, testhead calibration fixture 1314 is always identically positioned when itis set on top of test head 120.

Test head calibration fixture 1314 includes a plurality of calibrationpins 1324 which correspond to the location of alignment pins 1005. Eachprotection plate 1012 is moved so that each alignment hole 1020 isprecisely engaged by a respective calibration pin 1324. Once eachprotection plate 1012 is properly positioned, the screws holding eachprotection plate 1012 to test head 110 are tightened.

Once each protection plate 1012 is properly positioned, each LVDT iscalibrated relative to the top surface of contacts 14. This calibrationis desirable to provide the electronics (e.g. processor system 1090,described below) with signals generated by each LVDT 1015 whichrepresent how far each LVDT's spring loaded pin is pressed inward intoeach LVDT when each LVDT's spring loaded pin is at the same height ascontacts 14. As previously described, contacts 14 may be, for example,pogo pins (collapsible, spring-like pins) or static pins (e.g., as in aHypertac connector arrangement). Each LVDT 1015 is physically movedupward or downward within protection plate 1012 and is then secured intoplace so that each LVDT's spring loaded pin makes contact with the testhead calibration fixture 1314 and is pressed inward into each LVDT (e.g.by one tenth of an inch) so that each LVDT's pin is in operating rangewithin the LVDT and each LVDT begins to register. Thus, each LVDT'sspring loaded pin is aligned with the top of each of the pogo pins (in anon-compressed state). The signal generated by each LVDT (correspondingto the amount by which each LVDT's pin is pressed inwards) is thenstored in the electronics (e.g. processor system 1090). This signal isdefined as corresponding to the desirable inward compression of eachLVDT's pin instantaneously prior to mating of contacts with 14 toconnectors 15 during docking of test head 110 to device handler 120. Thetest head calibration fixture 1314 is removed.

Because calibration pins 1324 and calibration openings 1322 are formedin corresponding positions in calibration fixtures 1313, 1314, thecalibration procedure set forth above results in alignment pins 1007 andalignment holes 1020 relatively coinciding to facilitate accuratedocking of contacts 14 and connectors 15.

Once alignment pins 1007 and alignment holes 1020 are properlypositioned, the various lock screws included in positioner system 200are loosened so that positioner system 200 may move test head 110 withsix degrees of motion (X, Y, Z, θX, θY, θZ) so that alignment holes 1020on test head 110 are engaged by alignment pins 1005 on device handler120. Motion in the Z direction is accomplished by actuating motor 212.Motion in the θY direction is accomplished by actuating motor 132.Motion in the θX direction is accomplished by loosening lock screw 503(or loosening lock screws 628 and turning pitch adjust screws 615a,b).Motion in the X direction is accomplished by loosening lock screw 512(or loosening lock screws coupled to horizontal rail 51). Motion in theY direction is accomplished by loosening lock handle 4b. Motion in theθZ direction is accomplished by loosening lock handle 3 (or looseningthe screws going through slots 651).

After installation has been completed, movement of the test head 110 infour degrees of motion (i.e. the non-motorized degrees of motion) willbe restricted until a new installation (i.e., change in alignmentbetween test head 110 and device handler 120) is required. In thismanner, accurate docking between test head 110 and device handler 120when test head 110 is in actual operating use is accomplished strictlyunder motor control as provided by stepper motors 132 and 212. In thismanner, as explained below, fully automated docking of test head 110 todevice handler 120 is obtained.

Misalignment during automated docking between test head 110 and devicehandler 120 will result in misalignment between alignment hole 1020 andrespective alignment pin 1005. Misalignment between alignment hole 1020and respective alignment pin 1005, as previously explained, will resultin load detection from load cell 1010. Thus, the detection of load fromload cell 1010 indicates misalignment between test head 110 and devicehandler 120 and docking can be aborted until the cause of themisalignment is repaired.

FIG. 11 is a perspective drawing which shows the electronics cabinet1000 with its various electrical components which enable the automateddocking of test head 110 to device handler 120. Relays 1122, 1124actuate the various motors. Step up auto transformer 1070 converts 115volt AC to 230 volt AC (for use, again, by the motors--alternatively, ifthere is 230 volt AC service a step down transformer may be included toprovide 115 volt AC). Power supply 1060 provides a 24 volt DC output.This 24 volt DC output is used for powering limit switches 80a,b (onhorizontal member 8), limit switch 135 (on the roll axis), a switch (notshown) on device handler 120, a switch (not shown) on the test head,brakes 115, 131 and a relay contact in the light screen. Driver 1121 isused for driving stepper motor 132. Driver 1123 is used for drivingstepper motor 212. Power supply 1065 is used for powering LVDT 1015,load cell 1010, inclinometer 512, and inclinometer 510. Processor system1090 is also included.

The inter-relationship with the various electrical components shown inFIG. 11 is more clearly illustrated by FIG. 12. As shown in FIG. 12,processor system 1090 includes processor module 1110 (e.g., modelSLC5/03 manufactured by Allen Bradley Corporation), input module 1101,input module 1102, input module 1103, output module 1104, and inputmodule 1105 (e.g. all also manufactured by Allen Bradley Corporation).Input module 1101 receives input signals from inclinometers 510 and 512.Input module 1102 receives input signals from load cell 1010. Inputmodule 1103 receives input signals from LVDT 1015. Monitor 48 (alsoshown in FIG. 2) is also included. Processor module 1110 receives inputdata from, and transmits display data to, monitor 48. Input module 1105receives input data from contacts 80a, b and limit switch 135. Outputmodule 1104 transmits signals to indexer 1120. Indexer 1120 communicateswith driver 1121 which results in actuation of stepper motor 132.indexer 1120 also transmits signals to driver 1123 which results inactuation of stepper motor 212. Output module 110 transmits signals tosolid stat e relays 1130 to release and apply brakes 131 and 115. Theoptical circuits of light circuit 94 may transmit a light interruptionsignal to controller 1140. Controller 1140 can then transmit a signal tosolid state relays 1130 resulting in brake 131 and brake 115 beingapplied. Output module 1104 also transmits signals to relays 1122 and1124 to switch the output signals of drivers 1121 and 1124 between thepresent positioner system (stage 1) and an additional positioner system(stage 2).

Indexer 1120 is also capable of transmitting a signal indicative of therotation of stepper motor 132 and stepper motor 212. A signal generatedby indexer 1120 indicative of the rotation of the stepper motors can betransmitted into input module 1105 for use by processor system 1090.

Thus, a variety of mechanisms are used in order to determine the actuallocation of test head 110. Vertical position is detected in one ofseveral ways. When the test head 110 is initially being lowered towardsdevice handler 120, the (coarse) vertical position of test head 110 isinitially determined as a result of signals generated by inclinometer510. Specifically, processor system 1090 is programmed with therelationship between the vertical position of test head 110 and theangular position of linkage structure 20b. Thus, when processor system1090 receives signals from inclinometer 510, processor system 1090converts these signals into the vertical position of test head 110. Astest head 110 approaches device handler 120, the position of test head110 is determined using LVDTs 1015. As each LVDT 1015 makes contact withthe respective alignment pin base 1007 and test head 110 continues tomove towards device handler 120 the pin extending from each LVDT 1015 ispushed inwards. Each LVDT then transmits a signal to processor system1090 indicative of the distance by which each LVDT's spring loaded pinis pressed inwards. The more each LVDT's spring loaded pin is pressedinwards (i.e., the greater the compression--distance of each LVDT) thecloser test head 110 is to device handler 120.

The LVDTs (identified again as LVDT1, LVDT2, LVDT3, and LVDT4) can beused to measure roll, pitch and compression of the test head.

Roll measures the difference in distance between the right side 110a ofthe test head 110, and device handler 120 and the distance between theleft side of 110b of test head 110 and device handler 120. Roll ispositive when right side 110a is lower then left side 110b. In anexemplary embodiment of the present invention, the measurement is inmilli-inches. Roll is calculated in accordance with equation 1.

    roll= (LVDT3+LVDT4)-(LVDT1+LVDT2)!/2                       (1)

Pitch measures the difference in distance between the rear side 110d oftest head 110 and device handler 120 and the distance between the frontside 110c of test head 110 and device handler 120. Pitch is positivewhen the rear side hod is higher then the front side 110c. In anexemplary embodiment of the present invention, the measurement is inmilli-inches. Pitch is calculated in accordance with equation 2.

    pitch= (LVDT2+LVDT3)-(LVDT1+LVDT2)!/2                      (2)

Compression measures the average distance between each side 110a-d oftest head 110 and device handler 120 (i.e., the averagecompression--distance of the LVDTs). In an exemplary embodiment of thepresent invention, this measurement is made in milli-inches. Compressionis calculated according to equation 3.

    compression=(LVDT1+LVDT2+LVDT3+LVDT4)/4                    (3)

Using the LVDTs and the inclinometers, it is possible to "teach" thetest head to be in one of several positions with regard to the devicehandler. These positions could be defined as follows:

docked: the docking surface of the test head is facing and in contactwith the docking surface of the device handler;

undocked: the docking surface of the test head is facing the dockingsurface of the device handler, but separated from it;

manual: the test head is separated from the device handler. The dockingsurface of the test head is perpendicular to the docking surface of thedevice handler; and

maintenance: the test head is separated from the device handler. Thedocking surface of the test head is rotated 180° away from the dockingsurface of the device handler.

In order to perform automatic docking of test head 110 with respect todevice handler 120, processor module 1010 is "taught" the dockedposition of test head 110 after the initial mechanical installation andalignment of test head 110 and device handler 120 (previously described)has been accomplished. Processor 1010 is "taught" the docked position oftest head 110 after calibration of alignment pins 1005 and alignmentholes 1020 as previously described and relative to device handler 120 asfollows.

As shown in FIG. 13c at step 1300, the positioning of alignment pins1005 and alignment holes 1020 as previously described is accomplished.At step 1301, each LVDT is calibrated relative to the height of contacts14 as previously described with reference to FIG. 13a. At step 1302,stepper motors 132, 212 are manually actuated in order to bring testhead 110 approximately parallel to device handler 120. To actuate thesemotors, operator terminal 48 is programmed with push buttons MOVE UP,MOVE DOWN, ROLL COUNTERCLOCKWISE (CCW) and ROLL CLOCKWISE (CW) foractuating the respective motor in the appropriate direction. The testhead is then lowered until each of the LVDTs begin to make contact withthe device handler and each LVDT begins to compress. As test head 110 islowered, the speed of stepper motor 212 is decreased. Next, at step1303, the MOVE DOWN push button is depressed to lower the test headuntil all of the LVDTs are within operating range (e.g., plus or minus0.2500 inches). At step 1304, the ROLL CCW and ROLL CW push buttons aredepressed until a roll value of 0 is established. ROLL CCW makes theroll more negative. ROLL CW makes the roll more positive. At step 1305,test head 110 is raised manually moved along the X axis to reduce thepitch to 0. This is accomplished by loosening locks group 503. The rollis then checked and readjusted if necessary. At step 1306, the MOVE DOWNpush button is depressed to lower test head 110 so that the pogo pinscomprising contacts 14 are compressed (as determined by the signalsgenerated by the LVDTs) by a desired distance (or the male connectors ontest head 110 are inserted into the female connectors on device handler120 by a desired distance). Roll and pitch are then readjusted asnecessary. At step 1307, when the desired docking position has beenachieved, a TEACH DOCKED push button on operator terminal 48 isdepressed. This stores the roll, pitch and compression settings of theLVDTs in a memory of processor module 1110.

With regard to step 1306 (described above) there are various teachingsin the art as to how close test head 110 and device handler 120 shouldbe. This distance is carefully measured because this distance relates tothe total distance by which pogo pins (if contacts 14 are pogo pins) arecompressed or the total distance (if contacts 14 are male/femaleconnectors) by which the male connectors are inserted into the femaleconnectors counterparts). The distance by which the pogo pins should becompressed (or the male connectors inserted into the female connectors)will vary widely depending upon the manufactures and specifications ofthe pogo pins (or male/female connectors). However, the pogo pins willtypically be compressed 80% of total available stroke (or the maleconnector will be inserted 80% of the female connector's depth). Thus,by measuring the distance between test head 110 and device handler 120by using each LVDT 1015, test head 110 can be lowered for the desireddistance of compression of the pogo pins (or insertion depth usingmale/female connectors).

Once the docked position of test head 110 relative to device handler 120has been "taught" to processor module 1110, test head 110 canautomatically be docked to device handler 120. This is accomplished asfollows with reference to FIG. 14. At step 1401, a DOCK push button onoperator terminal 48 is depressed. If based on the reading ofinclinometer 510 the test head is below a predetermined level, the testhead is raised. This avoids test head 110 making contact with devicehandler 120 accidently while test head 110 is being rotated. At step1402, processor system 1090 transmits appropriate signals to indexer1120 for stepper motor 132 to roll test head 110 to an initial rollposition. At step 1403, processor system 1090 transmits signals toindexer 1120 for stepper motor 212 to move test head 110 down until allLVDTs have made contact and are within operating range. At step 1404,processor system 1090 test head 110 clockwise or counter clockwise asrequired until the roll condition matches the "taught" roll positionwithin plus or minus a preprogrammed amount (e.g. 0.002"). At step 1405,processor system 1090 provides appropriate signals for stepper motor 212to move test head 110 down until the compression matches the taughtcompression within plus or minus a preprogrammed amount (e.g. 0.002").Steps 1403-1405 may be iterated until both roll and compression arewithin plus or minus a preprogrammed amount (e.g. 0.002") of their"taught" values.

Misalignment during automated docking between test head 110 and devicehandler 120 will result in misalignment between alignment hole 1020 andrespective alignment pin 1005. Misalignment between alignment hole 1020and respective alignment pin 1005, as previously explained, will resultin load detection from load cell 1010. Thus, the detection of load fromload cell 1010 indicates misalignment between test head 110 and devicehandler 120 and docking can be aborted until the cause of themisalignment is repaired.

As previously described, the test head may be in the manual ormaintenance positions. An "undocked" position, with test head 110 movedaway from device handler 120 also exists. Each of these positions may be"taught" to processor from terminal 48. Specifically, the test head israised to the desired height and rolled to the desired orientation usingMOVE UP, MOVE DOWN, ROLL CCW and ROLL CW push buttons. TEACH UNDOCKED,TEACH MANUAL, and TEACH MAINTENANCE push buttons may then be depressedto store the respective positions of test head 110 within processorsystem 1090. Once processor system 1090 has been "taught" the undock,manual and maintenance positions, these positions may be automaticallyachieved by pressing the respective push buttons on monitor 48. In eachcase, when the appropriate push button is pressed, the test head isusually raised to its top most position, rolled to the "taught"orientation, and then lowered to the "taught" height. It is desirable toraise the test head to its top height (or near its top height) beforerolling the test head to assure adequate clearance between the test headand the device handler.

FIGS. 15-30 are flow chart diagrams which illustrate with some level ofdetail, the operation of processor module 1110 within processor system1090. FIG. 15 illustrates routines for updating position information,updating the position display on monitor 48, testing load cells 1010,testing for major faults, testing for light screen faults, and testingfor limit faults. FIG. 16 relates to screen management within monitor48. FIGS. 17a and 17b also relate to screen management for monitor 48.FIG. 18 relates to control of stepper motors 212 and 132 while the testhead is being moved. FIG. 19 relates to screen management on monitor 48.FIG. 20 relates to the display of monitor 48 and translating thedepression of certain push buttons on monitor 48 into physical motion ofthe test head. FIG. 21 relates to display update and push buttonmanagement for monitor 48. FIG. 22 relates to detection of push buttondepression in monitor 48 and storing "taught" positions. FIG. 23 alsorelates to detection of push button depression in monitor 48. FIG. 24relates to data received from inclinometer 512. FIGS. 25 and 26 relateto moving the test head up and down respectively. FIG. 27a, b relates tostoring values relating to updating LVDT 1010, pitch, compression andinclinometer 510. FIGS. 28-30 relate to actuation of motor 132.

As previously described, numerous safety mechanisms are included inorder to avoid injury to the operator and damage to the equipment. Forexample, brakes 115, 131 are locked when AC power is removed from thesystem. Brakes 115 are locked before the start of vertical motion alongthe Z axis, and immediately after completion of vertical motion alongthe Z axis. Brakes 131 are locked before the start of motion about the Yaxis, and immediately after completion of motion about the Y axis.

As previously stated, a light screen is included. If the light screen ispenetrated, brakes 115, 131 lock immediately.

As previously stated, limit switches 80a,b are also included. Theselimit switches detect the ends of permissible travel of trolley 17c. Theoutput of limit switches 80a,b sensed by processor system 1090 via inputmodule 1105. If a limit condition is detected, any automatic motion inprogress is halted, a fault message is displayed, and further motioninto the limit is inhibited. There are also software limits narrowerthan the switch limits. An external emergency stop switch may also beincluded. Actuation of the external emergency stop switch locks allbrakes and opens the AC line, removing AC power from the apparatus.

The invention has been described with each alignment pin base 1007 (eachwith alignment pin 1005) mounted on device handler 120 and eachprotection plate 1012 (each with alignment hole 1020) mounted on testhead 110. However, as would be apparent to one of ordinary skill in theart, this order can be reversed so that each alignment pin base 1007(with alignment pin 1005) is mounted on test head 110 and eachprotection plate 1012 (with alignment hole 1020) is mounted on devicehandler 120. A load cell 1010 would thus be under each alignment pin1005 and coupled to test head 110. Each LVDT 1015 would remain coupledto test head 110. Each LVDTs pin is depressed inward into each LVDTafter making contact with protection plate 1012. This embodiment isillustrated, for example, by FIG. 31a. Alternatively, as shown in theembodiment illustrated by FIG. 31b, each LVDT 1015 may be mounted intoeach protection plate 1012 on device handler 120. Each LVDTs pin isdepressed inward into each LVDT after making contact with alignment pinbase 1007.

In a further alternative embodiment, illustrated, for example, by FIG.31c, each alignment hole 1020 is formed in a protection plate 1012 whichis attached to test head 110 and each alignment pin base 1007 withalignment pin 1005 is attached to device handler 120. Each LVDT 1015 isattached to device handler 120 instead of being attached to test head110. Each LVDTs pin is depressed inward into each LVDT after makingcontact with protection plate 1012.

The invention has been described with a load cell 1010 under eachalignment pin 1005. However, one of ordinary skill in the art wouldrecognize that load cell 1010 could be used in conjunction withalignment hole 1020 instead. For example, alignment hole 1020 could bethe opening of a floating bushing installed within protection plate1012. Load cell 1010 could be appropriately positioned relative to thefloating busing so that movement of the floating bushing relative toprotection plate 1012 results in a load on load cell 1010. Thus, forexample, if alignment pin 1005 does not accurately engage alignment hole1020 (i.e. pin 1005 engages hole 1020 at an angle or not at all), loadcell 1010 would signal a load (indicative of inaccurate docking). Inthis manner, accurate docking between contacts 14 and connectors 15 isagain ensured.

The invention has been described with the use of LVDTs to determine theposition of test head 110 relative to device handler 120. However, othertypes of proximity sensors (non-linear but repeatable sensors) may besubstituted for the LVDTs. For example, optical type sensors may be usedto determine the position of test head 110 relative to device handler120. Furthermore, in place of inclinometers, angular position encoders(e.g. Allen Bradley Bulletin 845C) can be attached to any of the parts(e.g., gears, lead screws) rotated by motors 132, 212. The amount ofrotation sensed by the angular position encoders can be translated intothe distance of travel of test head 110 in order to determine thelocation of test head 110. Furthermore, the inclinometer used to measurevertical position via the angle of linkage arm structure 20b could bereplaced with a variety of linear position encoders. All thesubstitution set forth above could be readily accomplished by one ofordinary skill in the art.

In addition, although the invention has been described with the use offour LVDTs, in accordance with a further exemplary embodiment of theinvention, only three LVDTs may be used. As shown in FIG. 32, the LVDTscan be arranged in (for example) a triangular pattern with two LVDTstowards the front of test head 110 and one LVDT towards the rear of testhead 110. Of course, this pattern can be reversed (one LVDT in the frontand two LVDTs in the rear). With regard to the arrangement shown in FIG.32, the LVDTs (identified as LVDT1, LVDT2, and LVDT3) can be used todetermine the previously defined pitch, roll and compression values oftest head 110 relative to device handler 120 according to equations 4,5, and 6 respectively:

    Pitch= (LVDT1+LVDT2-2*LVDT3)/2!                            (4)

    Roll=LVDT2-LVDT1                                           (5)

    Compression= (LVDT1+LVDT2+LVDT3)/3!                        (6)

In addition, a fourth LVDT may be included for redundancy to ensure thatthe remaining LVDTs are providing correct readings.

The invention has been described with the LVDTs externally attached totest head 110. However, one skilled in the art would readily recognizethat the LVDTs can be incorporated into (i.e. be an integral part of)test head 110. Thus, by sufficiently miniaturizing the LVDTs, the LVDTsmay be located within the periphery of test head 110. For example, theLVDTs may be located among contacts 14.

The invention has been described with regard to stepper motors foraccomplishing motorized motion. In alternate exemplary embodiments ofthe present invention, a pneumatic motor or a hydraulic motor may beused. However, one skilled in the art would readily recognize that themotor can be supplemented with a counter balance system bearing the loadof the carriage base 26 with the test head 110 attached. In this manner,operator and equipment safety may be enhanced.

The invention has been described with regard to a single positionersystem. However, additional positioner systems, incorporating forexample support members 9 and 10, may be used adjacent to the positionersystem presently illustrated in the figures.

While the invention has been described in terms of an exemplaryembodiment, it is contemplated that it may be practiced as outlinedabove with modifications within the spirit and scope of the appendedclaims.

What is claimed:
 1. A positioner for docking and undocking an electronictest head with a device handler comprising:head rotation means forrotating said electronic test head about a first axis; motion means,including a plurality of arm structures coupled to said head rotationmeans; a first one of said plurality of arm structures coupled to asecond one of said plurality of arm structures to form a scissor shapedmember of increasable and decreasable length for moving said electronictest head along a second axis orthogonal to said first axis;inclinometer means coupled to at least one of said plurality of armstructures for providing a signal corresponding to angular orientationof said at least one arm structure; and processing means for convertingsaid signal to a measurement of distance between said test head and saiddevice handler.
 2. A positioner according to claim 1, wherein aplurality of alignment pins are affixed to one of said electronic testhead and said device handler and a plurality of alignment holes areformed in another of said electronic test head and said device handler,each of said plurality of alignment pins extending into a respective oneof said plurality of alignment holes when said electronic test head isdocked with said device handler.
 3. A positioner according to claim 1,further comprising sensor means for determining distances between aplurality of locations on a surface of said electronic test head and arespective plurality of locations on a surface of said device handlerand for generating signals corresponding to said determined distances.4. A positioner according to claim 3, wherein said sensor meansgenerates four signals identified as LVDT1, LVDT2, LVDT3 and LVDT4, eachof said four signals corresponding to a respective one of said distancesbetween said plurality of locations on said surface of said electronictest head and said respective plurality of locations.
 5. A positioneraccording to claim 3, wherein said head rotation means rotates saidelectronic test head about said first axis and said motion means movessaid test head along said second axis responsive to said signalsgenerated by said sensor means.
 6. A positioner according to claim 4,wherein said head rotation means rotates said electronic test head aboutsaid first axis and said motion means moves said test head along saidsecond axis based upon pitch and roll of said electronic test headrelative to said device handler wherein pitch is calculated as:

    pitch= (LVDT2+LVDT3)-(LVDT1+LVDT4)!/2

and roll is calculated as:

    roll= (LVDT3+LVDT4)-(LVDT1+LVDT2)!/2.


7. A positioner according to claim 2, further comprising a plurality oftransducers each located under a respective one of said plurality ofalignment pins, wherein misalignment between said plurality of alignmentpins and said plurality of alignment holes results in said transducersgenerating signals indicative of said misalignment.
 8. A positioneraccording to claim 1, further comprising movement means for at least oneof:a) moving said test head along said first axis; b) moving said testhead about said second axis; c) moving said test head along a third axisorthogonal to both said first axis and said second axis; and d) movingsaid test head about said third axis.
 9. A positioner according to claim1, wherein said head rotation means and said motion means are powered.10. A positioner according to claim 3, wherein said sensor meansincludes a plurality of sensors, further comprising calibration meansfor calibrating each of said plurality of sensors to generate respectivepredetermined signals upon docking of said electronic test head and saiddevice handler.
 11. A positioner according to claim 3, furthercomprising a calibration fixture for positioning one of said alignmentpins and said alignment holes relative to the other of said alignmentpins and said alignment holes.
 12. A positioner according to claim 10,further comprising a calibration fixture for positioning one of saidalignment pins and said alignment holes relative to the other of saidalignment pins and said alignment holes.
 13. A positioner according toclaim 3, wherein said electronic test head and said device handler eachinclude respective contacts, said sensor means includes a plurality ofsensors, and each of said plurality of sensors are located between arespective two of said contacts on one of said electronic test head andsaid device handler.
 14. A positioner according to claim 3, wherein saidsensor means generates three signals identified as LVDT1, LVDT2 andLVDT3, each of said three signals corresponding to a respective one ofsaid distances between said plurality of locations on said surface ofsaid electronic test head and said respective plurality of locations.15. A positioner according to claim 14, wherein said motion means movessaid test head in a vertical direction and said head rotation meansrotates said electronic test head about said first axis based upon pitchand roll of said electronic test head relative to said device handlerwherein pitch is calculated as:

    Pitch=(LVDT1+LVDT2-2×LVDT3)/2

and roll is calculated as:

    Roll=LVDT2-LVDT1.


16. A method for docking an electronic test head with a device handler,comprising the steps of:rotating said electronic test head about a firstaxis; moving said test head along the second axis orthogonal to saidfirst axis by increasing and decreasing length of a scissor-shapedmember which includes a plurality of arm structures; providing a signalcorresponding to angular orientation of at least one of said pluralityof arm structures; and converting said signal to a measurement ofdistance between said test head and said device handler in order to docksaid electronic test head with said device handler.
 17. A method fordocking an electronic test head with a device handler according to claim16, wherein said test head includes contacts, and a plurality of sensorsare secured to at least one of said test head and said device handlerfor determining respective distances between said plurality of locationson said surface of said test head and said respective plurality oflocations on said surface of said device handler, said method furthercomprising the steps of:providing a calibration fixture having a planarsurface; placing said planar surface of said calibration fixture ontosaid contacts so that said calibration fixture extends directly abovesaid plurality of sensors, and adjusting each of said plurality ofsensors to contact said calibration fixture and generate a respectivecalibration signal defining docking between the test head and the devicehandler.